The increasing demand for certain olefins as chemical intermediates for the production of oxygenates and alkylates for motor fuels, coupled with the plentiful supply of lower alkanes, provides incentive for the use of catalytic dehydrogenation on an industrial scale: E. Chang, in "Alkane Dehydrogenation and Aromatization", Report No 203, SRI International, Calif., Menlo Park, 1992.
Driven largely by the rapid growth in demand for tertiary alkyl ethers, the dehydrogenation of isobutane or isopentane to isobutylene or isoamylene respectively is receiving renewed attention since branched ethers are prepared by etherification of branched olefins with methanol or ethanol.
The dehydrogenation reaction is currently carried out in commercial processes in the vapor phase over chromia-alumina or noble-metal catalysts. Due to the endothermic nature of this reaction and the normally unfavorable equilibrium, elevated process temperatures are necessary to reach economically acceptable levels of conversion. These severe operating conditions favor coke formation and catalyst deactivation. As a consequence, most of the commercial processes for dehydrogenation of lower alkanes require feeds diluted with hydrogen or steam and short reaction cycles with frequent regenerations: Chang, supra; A. J. Horsley, in "Catalytic Dehydrogenation and Oxidative Dehydrogenation", Catalytica Study No. 4190 DH. Catalytica, Calif., Mountain View 1991. Improved process economics could result from the development of catalysts that perform well under severe conditions for deactivation.
Previous workers have shown that the addition of small amounts of sulfur to certain metallic catalysts has beneficial effects on selectivity and coke formation. For example, R. J. Rennard, and Freel, J. Catal., 98, 235 (1986) have shown that sulfur causes an increase in propylene yield over Pt-Re catalysts upon sulfiding. The effect of sulfur in reducing the rate of coke formation has been reported by Rostrup-Nielsen and co-workers: J. R. Rostrup-Nielsen, and I. Alstrup, in "Catalysis 1987" (J. W. Ward, Ed.) p. 725, Elsevier, Amsterdam, 1988; Rostrup-Nielsen, J. Catal., 85, 31 (1984); Alstrup, Rostrup-Nielsen, and S. Roen, S. Appl. Catal., 1, 303 (1981); Rostrup-Nielsen, and K. Pedersen, J. Catal., 59, 395 (1979); and Rostrup-Nielsen, J. Catal., 27, 343 (1972), for Pt-Re catalysts and for the case of steam reforming. The presence of half a monolayer of sulfur on the Ni surface strongly inhibited the rate of carbon deposition, while it did not inhibit the rate of steam reforming to the same extent. This effect has been explained in terms of the ensemble of atoms required to constitute the active site for each reaction. The ensemble for the steam reforming reaction is smaller than that required for coke formation. Consequently, although both rates decreased when sulfur was added, the coking rate did so almost 10 times faster than the reforming rate.
Reducing nickel-impregnated alumina in hydrogen without prior calcination in air resulted in greater nickel surface area and dispersion than found in those catalysts obtained by reduction with prior calcination in air; C. H. Bartholomew and R. J. Farrauto, "Chemistry of Nickel-Alumina Catalysts", Journal of Catalysis, 45, 41 (1976).
Calcining nickel-impregnated catalyst prior to reduction in hydrogen is disclosed in J. F. LePage et al, "Applied Heterogeneous Catalysis", page 110, Gulf Publishing Company, Houston (1987).
The mechanisms of sulfiding pre-reduced and pre-oxidized nickel particles have been studied by P. J. Mangnus, E. K. Poels, A. D. Langeveld and J. A. Moulijn, "Comparison of the Sulfiding Rate and Mechanism of NiO and Ni.sup.0 Particles", Journal of Catalysis, 137, 92 (1992). Commercial theta-alumina-supported nickel catalysts were reduced to Ni.sup.0 and sulfided. A green NiO catalyst based on alpha-alumina was calcined and then sulfided.
NiO "well dispersed" and relatively strongly bound on a gamma-alumina support is disclosed in B. Scheffer, P. J. Mangnus and J. A. Moulijn, in Journal of Catalysis, 12, 18 (1990) .
Sulfiding catalytic nickel in situ as formed in the dehydrogenation of butene with a nickel-phosphate containing catalyst is disclosed in H. E. Swift, H. Beuther and R. J. Rennard, "Elimination of Excessive Carbon Formation During Catalytic Butene Dehydrogenation", Ind. Eng. Chem., Prod. Res. Dev., 15, No. 2, pages 131-135 ((1976).
A compound containing reduced or oxidized nickel on kieselguhr used in catalysis of dehydrogenation and hydrogenolysis of cyclohexane is disclosed in V. D. Stytsenko et al, "Production of Active Surface of a Nickel-Tin Catalyst for Dehydrogenation of Hydrocarbons", in "Kinetics and Catalysis", Consultants Bureau, N.Y., Plenum Publishing Corporation, pages 802-807 (1988).
Catalysts containing nickel in an oxidized or reduced state are disclosed in M. Agnelli et al, "Surface Organo-metallic Chemistry on Metals. Preparation of New Selective Bimetallic Catalysts by Reaction of Tetra-n-butyl Tin With Silica Supported Rh, Ru and Ni", in Catalysis Today, 9 (1989) 63-72.